This invention relates to a method of manufacturing a shell for a universal-joint and an apparatus therefor, and more particularly to that when a shell is made by press forming process.
As a species of universal-joints for flexibly joining a pair of rotary shafts, one is known wherein a tubular shell having a flange on one end thereof is secured at the flange to one of the rotary shafts and the other rotary shaft is inserted inside the shell for being engaged, through a plurality of engaging members disposed at the inserted end thereof, with a plurality of grooves axially extended inside the shell so that the pair of rotary shafts can be rotatably connected.
In some universal-joints belonging to this category, a shell has been conventionally manufactured by forming a hollow cylindrical material or blank of thick wall through extrusion such as hot forging or cold forging, followed by a forging process applied on the thick walled material with a punch and a die and a machining process for forming the grooves to a desired shape and dimension.
The above-mentioned manufacturing method is problematical in various respects, for example, being low in productivity because of its laborious and time-consuming process of machining when finished, consequent cost rising, or deterioration of strength of the products because of machining or cutting of the material after the forging.
Adoption of the forging process which is inherently required to be large in the wall-thickness inevitably makes the products to be thick-walled in the above-mentioned method, which necessitates the products heavy and expensive in material cost, to a great disadvantage.
The above-described disadvantage inherent to the shell manufacturing method is due to the manufacturing method depending on forging and the consequent machining. The Inventors of this invention then thought of an idea before to manufacture the shell from a thin walled cylindrical material or blank by means of applying a press forming process thereon. An application for patent to a completed method for this purpose after a series of studies and experiments in respect of concrete conditions and required order of processes was filed with the Japanese Patent Office with the Serial No. TOKU-GAN-SHO-55(1980)-69499, on which was filed an International Patent Application No. PCT/JP81/00079 which was published as WO No. 81/03294, and on which an European Patent Application No. 81 900 944.0 was filed on Jan. 21, 1982, and a U.S. patent application Ser. No. 342,010 on Jan. 15, 1982. The gist of that invention resided in applying a preliminary pressing process on a cylindrical material so as to form a plurality of grooves extended in an axial direction and also applying simultaneously or thereafter an ironing process along the longitudinal grooves so that the grooves may be finished into desired dimension and shape.
This method was not perfect because of including two kinds of processes, namely the pressing process and the ironing process, which naturally necessitated respectively different sets of dies and required double man-hours.